Process for obtaining metal coatings on articles of aluminum and aluminum alloys



the action of a weak electric current in an dipping in a solution of thefluoride of the:

Pasta Ne 1926.

UNITED STATES PATENT oFFlcaf nomnur. mm, or BERLIN, onnmnmr. nssronon Torun 1mm nn. orro srn'nnonn, rnrnurvnnwnn'rune JIRO'I'KA MIT nnsonnanxrnnRamona. or

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PROCESS FOR OBTAINING METAL COATINGS ON ARTICLES. 01 ALUMINUM All!)ALUMINUM ALLOYS.

No Drawing; Application filed January 15. 1926, Serial No. 81,580, andin Germany October 29, 1924.

It is known to coat aluminum articles very thinly with copper, on whicha thicker coating of nickel'or the like can be electrically depositedwithout the danger of the peeling Off which occurs when the nickel isdeposited directly on to the aluminum. To effect such thin coating withcopper the aluminum articles, after they have been separately freed romgrease, are exposed to acid bath of a copper salt.

' In the art of coating. metals it has also been proposed to coataluminumwith a preliminary layer of copper, zinc, or tin, by

coating metal and potassium tartrate. It has been further proposed tocoat-aluminum preliminarily with zinc by dipping the aluminum insulphate of zinc and ammoniuin tartrate.

-' muth, silver,

',mixture of the salts- It has, also been proposed to coat alumi- 1 numdirectly with a desired metalbydipping ,in'a bath, which maybe heated tohasten the action,' "composed of ammonium coating metal,the bath beingrendered alka line by the addition of liquid or aqua animonia, orammonium carbonate. A mixed coating may' be obtained by using asuitab'leof the coating metals. According to the present invention a usable metalcoating is obtained on alumi num both without preliminary freeing fromgrease and without employment of electric current byimmersion in abath-oi hot. salt solution of alkaline reaction, which contains salts ofcopper, nickel, cobalt andzinc,

bisgold and tin and in addition only potassium carbonate and potassiumbicarbonate alone, or mixed with a. corresponding salt or salts ofsodium. Watersoluble-oxygen liberating compounds in parmanganese, ironand-chromium, lead,

.ticular water-soluble chromate canbe added- 45 to the bath.

dropper coatingv obtained in the presence of alkaline-carbonate has adark colour. A bright andlclean metallic deposit is obtained- ,if anoxidizing agent, in particular otassiumbiohromate, 1s added to the bat Abath which has chloride and the chloride or the salt of the coatingduralumin,

proved extremeigegood m use contains in' 2.5 litres of water 25 gms.

.of crystalline copper sulphate, 25 gms. of potassium carbonate, 25 gms..of sodium bicarbonate and 10 gms. of potassiumbichromate. Instead of 10gms. of potassium bi- .chromate up to 25 gms. of a 3% solution ofhydrogen peroxide can" be used. Instead of potassium carbonate andsodium bicarbonate a correspondingly greater quantity'of potassiumbicarbonate alone can be used.

In this bath the copper. sulphatecan'be replaced by, eqiiivalentquantities of inorganic salts of heavy metals, so that a firmly adheringdeposit can he obtained direct, that is without preliminary deposit of alayer of copper.

In this way it is possible by using the sulphate of nickel. cobalt,ormanganese, iron, chromium, ing metal'coatings on aluminum. The samemethod succeeds with nitrates of lead. bismuth or silver. The silvercoatin is at first bright, but with longer boiling ta es on theknown asso-called oxidized 'tained without the use of oxidizing agents.

The above mentioned metallic salts can also be used mixedto obtain mixedcoatings. For example a mixed deposit of chromium or zinc to.produceffirmly adher-.

obtained, which however bright appearance of the and silver can beobtained on soft aluminum by using a solution containing in 1 litre ofwater, 10 gms. of chromium sulphate, 2 gms. of silver nitrate, 10 gms.of ,potassium oars bon'ate, 3.3 gms. of sodium bicarbonate, and 3.3gms.. of potassium bichromate. For three times the quantity of eachconstituent lv n (e. g. 10;2o, is added. to the metallizin'g baths, Y

Instead of articles of pure aluminum,- those made of aluminum alloys, e.g.- dura-' lumin, can be coated.

It will be noted from theabove descripis used per litre. It has beenfound that the coatings are brighter written description theprocesshasth advantageithat neither the electric current nor prior cleaningisnecessary.

In certain of the claims the term a substantial amount of has been usedbefore the name of certain ingredients or compounds. Such terms havebeen used to distinguish from cases in which mere traces of('orinconsequential amounts of) the said substances may. possiblyhavebeen present asimpurities in other substances used.

What I claim is: 1. The process for producing'metal coating on aluminumor an aluminum alloy without substantial previous cleaning whichcomprises subjecting a surface thereof without application of electriccurrent to'the'action which comprises subjecting a surface thereofwithout application of electric current to 4 electronegative vtoaluminum.

of an aqueous liquid togwhich has been added a bicarbonate of an alkalimetal and a simple salt of a metal which is electronegative to aluminum.

' 2.- The process for producing metal coating on aluminum or an aluminumalloy which comprisessubjecting a surface thereof to the action of anaqueous liquid to which has been added a bicarbonate of an alkali metaland a salt of a metal which is. 'electronegative to aluminum. a

' 3. The process for. producing; metal coating on alumin or an aluminumalloy the action of an aqueous liquid to which has been added an alkalicarbonate, 'an alkalibicarbonate and a salt of a metal which is to theaction of an aqueous liquid containmg potassium bicarbonate and a saltof a a metal whichis electr'onegative'toialuminum.

' ing on aluminum or an;

6. The process for producing metal coataluminum alloy 'which' comprisessubjgting, a surface thereof to'theaction of an aqueous liquid to whichhas-been added carbonate ,of an alkali metal, a substantial amount ofbicarbonate of an alkali metal,'at least-one of said alkali metals beingpotassium, and a salt of a metal which is electronegative toalumiilinnf.

7 The process for prjoduciiig metal coating on at umfor aluminum alloywhich comprises subjecting a surface thereof a without application ofelectriccurrent to the metal which is electronegative to producing-metalcoatmg onv alummumor an aluminum to which has been added a bicarbonateof an alkali metal and a salt of a metal which is electronegativetoaluminum.

8. The process for producing metal coating on aluminum or an aluminumalloy -which compr ses subjecting a surface thereof to the action of anaqueous liquid to which has been added a' substantial amount ofbicarbonate of an alkali metal, and oxygen liberating compound and asimple salt of a metal which is elec'tronegative to aluminum.

9."The process for producing metal. coating fon aluminum or an aluminumalloy Ywithout substantial prior cleaning which comprises subjecting asurface thereof to the action of added a substantial amount ofbicarbonate of potassium, an oxygendiberating agent,

and salt-0f a metal which is electronegative to aluminum.

10. The process for producing metal coating on aluminum or an aluminumalloy which-comprises subjecting a surface thereof to the action of anaqueous liquid to which has been added .a. substantial amount ofpotassium bicarbonate, an oxidizing agent and a salt of a-metal which iselectronegative to aluminumr 11. Theprocess for producingmetal coatingon aluminum. or an aluminum alloy .which comprises subjecting a surfacethereof to the action of an has been added a carbonate of an alkalimetaqueous li uid s which a1; a bicarbonate of an alkali -metal at leastone of said alkali oxygen liberating compound 12. The-.process forproducing metal coat- .ing on aluminum or an aluminum alloy whichcomprises subjecting a surface thereof to the action of an aqueousliquid to which has been added a. bicarbonate of an alkali metal, anoxygen liberating agent and a salt of ametal-electronegative toaluminum, p I p 13. The process for producing metal coatmg onaluminum oran aluminum alloy which comprises subjecting a surface thereof to theaction of an aqueous liquid to which has been added a bicarbonate of analkali metal. a carbonate of an alkali metal,

an oxygen liberating compound and a salt of a metal which iselectronegative to aluminum. V

14. The process ior'producing metal coating on-jaluminum or analuminumalloy which comprises subjecting 'the surface thereof to the action ofan aqueous liquid added potassium bicarbonate, an. oxidizing compound,glycerine and a saltof a metal which is electronegative to aluminum,

15.;The process for producing metal coats ing on 3 aluminum I whichcomprises subjecting a surface. thereof metals being potassium. an

, and a salt of a aluminum.

or an aluminum alloy an aqueous liquid to which'has been I H sium,-anoxygen liberating compound,

alkali bicarbonate and a H which is elect-ronegative to 20. A bathmixture for coating aluminum or. an aluminum alloy by contact with anaqueous mixture-thereof containing a carlbonate of an alkali metal, asubstantial, g -famount of a'bica-rbona te of an alkali metal,

which comprises subjecting a surface thereof to the action of an aqueousliquid to which has been added a bicarbonate of'an alkali metal, anoxygen liberating agent, glycerine, and salt of a metal which iselectronegative to aluminum.

17. A bath mixture for coatingaluminum or an'aluminum alloy by contact'with an aqueous mixture thereof containinga sub-' stantial amountof abicarbonate of an alkali 0 metal and a'salt of a metal which iselectronegative to-aluminum. a

'18. A bath mixture for coating aluminum or an aluminum alloy by contactwith an aqueous mixture thereof containing a substantial amount ofpotassium bicarbonate and a salt of a metal which is ele'ctronegative toaluminum.

19. A bath mixture for coating aluminum or an aluminum alloy by contactwith an 0 aqueous mixture thereof containing-an alkali carbonate, asubstantial'amount of an aluminum.

at least one of said alkali metals being potassium, and a salt ofa metalwhich is electronegative to aluminum. i

, .21. A bathv mixture for coating aluminum or an aluminum allog bycontact with an I aqueous mixture thereof containing a bicary salt of ametal" bonate of an alkali metal, an oxygen liber. ating compoundand asalt of a metal which is electronegative to aluminum. I

22. A bath mixture for coating aluminum or an aluminum alloy by contactwith anaqueous mixture thereof containing potassium bicarbonate, anoxygen liberating compound and a salt of a metal which iselectronegative to aluminum.

23. A bath mixture for coating aluminum or an aluminum alloy by contactwith an aqueous mixture thereof containing a substantlal amount ofpotassium bicarbonate, an

alkali chromate compound, and a salt of a metal which is electronegat veto alumlnum.

, 24. A bath mixture for coating aluminum oran aluminum alloy by contactwith an aqueous mixture thereof containing a carbonate of an alkalimetal, a substantial amount of bicarbonate of an alkali metal, at leastone of said alkalimetals being potassium, an oxygen liberatingcompound,

and a salt of a metal which is electronegao tive to aluminum. 7

25. Abath mixture for coating aluminum or an aluminum alloyby-c'ontactwith an aqueous mixture thereof containing a carbonate of analkali metal, a substantial amount of bicarbonate of an alkali metal, atleast one of said alkali metals being potassium, an alkali chromatecompound, 7 and a salt of a metal-which is electronegative to aluminum.

2(5. A bath mixture for coating aluminum I or an aluminum alloy bycontact with an. 80.

aqueous mixture thereof cont-ainin' acar bonate of an alkal metal, a sustantial amount of bicarbonate of an alkali metal,

an oxygen liberating compound and a salt of'a metal which iselectronegative to aluminum.

' I In testimony whereof I aflix' my signature.

,BIOHUMIL JIR'OTKA.

